Democratic presidential hopeful Sen. Elizabeth Warren (Mass.) has released a plan to provide universal free child care to every American, paid for by a steep tax on those Americans she calls "ultra-millionaires."

What's the plan?

According to a news release on her Senate website, the Universal Child Care and Early Learning Act would provide federal funding for "a locally-run network of Child Care and Early Learning Centers and Family Child Care Homes so that every family, regardless of their income or employment, has high-quality, affordable child care options for their children from birth to school entry."

These centers would be available for free to people below 200 percent of the federal poverty line. Families with higher incomes would have to pay for these options, but not "more than seven percent of their income."

Warren said that she expected this plan to nearly double the number of children with access to formal child care, from 6.8 million to 12 million. The senator argued that the current "lack of access to high-quality, affordable care prevents parents from fully participating in the workforce, holding them back from career and educational opportunities and placing a drag on our entire economy."

Critics, however, argue that it's not clear what exactly the "high-quality" national standards Warren refers to in her plan are.

"In the wealthiest nation in the history of the world, high-quality child care should be a right for all of our children and not just a privilege that only the wealthiest families can afford," Warren said.

But how would she pay for it?

This plan would cost "$700 billion over 10 years" and would be funded by "approximately a quarter of the revenue raised from Senator Warren's proposed Ultra-Millionaire Tax," according to the news release. Presumably the total cost would far exceed that over time, since she proposed having the federal government continue to fund these centers in perpetuity.

This tax, according to a plan released by her presidential campaign in January, would put an additional 2 percent tax on any American worth more than $50 million, and a 3 percent tax on anyone worth more than $1 billion. This tax would target assets, rather than income.